Filament for incandescent lamps or similar articles



Nov. 29, 1927. 0 1,650,605

, Y P. A. CAMPBELL FILAMENT FOR INCANDESCENT LAMPS 0R SIMILAR ARTICLESFiled Dec. 9-, 1926 JNSZ'ENTUR. REE CY A. CAMPBELL,

firs ATI'UHNEYI STATES PT 2: 1;

PERCY A. CAMPBELL, 01 EAST CLEVELAND, OHIO,.ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION NEW YORK.

FILAMENT FOR INCANDESGENT LAMPS 0R SIMILAR ARTICLES.

Application filed December 9, 1926. Serial No. 153,665.

My invention relates to filaments forelectric incandescent lamps andsimilar devices, and to methods of their manufacture. St1ll moreparticularly my invention relates to coiled metal filaments, andparticularly those filaments which are subjected during use to hightemperatures and tend to warp and twist out of shape. ()ne of theobjects of my invention is to overcome this difficulty. Another objectof my invention is to facihtate the mounting of filaments and tominimize the chances for distortion of the filament during the mountingoperation.

According to the present practice where a mandrel wire is used in thecoiling of filaments, such mandrel wire is removed usually immediatelyafter the coiling and the mandrelless filament coil-is afterwardsmounted on the lamp stem and the ends thereof united to the leading-inconductors of the lamp as by welding or clamping. The handling of amandrelless wirecoil is comparatively difficult and such practice doesnot lend itself'to the use of automatic filament mounting machinery.When such filaments are mounted by hand, on account of their extremeflexibility they may be very easily distorted by the operator. Accordingto my invention, the mandrel wire is not removed until after i 30 thefilament has been mounted, on the lamp stem and its ends united to theleading-in conductors. This has the great advantage that the filament iseasily handled and distortion during the mounting operation isprevented. According to my invention, the mandrel wire is finallyremoved after the mounting of the filament, preferably by dis-.

solving in acid." i

It is the practice with coiled filaments to give the filament apreliminary set by raising to a high temperature. This has been done byfiring the mandrelless' filament coils at a high temperature approaching1600 C. in cases where-the'filament is subjected to exceptionally hightemperaturesin use. While in the case of my invention, this treatmentmay be given to the mandrel containing the filament before mounting, itmay als'o be given to the-filament after mounting and before the mandrelhas been removed. This has an additional advantage in that the final setis given to'the filament while it is still held firmly in a definiteposition.

In the drawing, Fig. 1 is an elevation of a filament coiled upon amandrel wire; Fig. 2

i'nanufacturc of a modified form of filament;-

Fig. 5 is an end elevation thereof; and Fig. 6

is an elevation of an electric incandescentlamp comprising said modifiedfilament.

As shown in Fig. 1, the filament wire 10 is coiled upon a mandrel wire11 which may be any wire which may be dissolved or otherwise removed. Iprefer to use molybdenum or other wire which will stand a fairly hightemperature. The filament coil 12 with its mandrel is preferably given aheat treatment to set the coil, and this may be done be fore or aftermounting the filament. The filament is mounted upon a stem 13 which, asshown, comprises the comparatively rigid conducting supports 1415 whichare preferably united to the ends of the filament by welding, asshown'in Fig. 6, although as hereinafter explained, they may be unitedby clamping as shown in Fig. 2. The sup port wires 14c15 may be ofchromium treated nickel. In Fig. 4 the mandrel containing the coiledfilament is wound upon a man drel 16 and ordinarily it is not necessaryto leave this mandrel in place, but a filament may be stripped therefrombefore mounting. However, it lends to greater definlteness in filamentform to allow said second mandrel to remain until after mounting of thefilament. In such case it is preferable to have such second mandrel tobe composed of molybdenum or other lugh heat resisting metal, whereas ifthe second mandrel is re electric current through the mandrel andfilament with the mount placed for instance, in a hydrogen bottle.

The removal of the mandrel is preferably accomplished by means of anacid which dissolves. it. One solution which may be candescent lampscomprising used is four parts of nitric acid, four parts of water, andone part sulphuric acid. Another solution which may also be usedconsists of four parts nitric acid and one part sulphuric acid. In usingthese solutions it is necessary to use support wires of a material whichis not readily attacked by these solutions. Tungsten is a suitablematerial. If the leading-in conductors are subjected to the acid, theyalso should be of tungsten or-other metal which is not afiected by theacid although the operation may be performed by dipping only thefilament and a portion of the supports in the acid, and in such casesonly the supports proper would have to be of acid resisting metal.Nickel may be used as a support or leading-in conductor, but in suchcase care would have to be t align tgflpreyent its being attacked toomuch by the mandrebdiesolvingaci,d.

Chromized nickel, nickel or a steel containing chromium or otherwiseprotected by chromium, 's preferable to pure nickel for this purpose.

In Figs. 3 and 6 are shown electric inbulbs 17' in which are sealed themounts comprising the stems 13. In each case the filament coil 12 isshown in its final shape after the mandrel has been removed.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of manufacturin and mounting coiled filaments forincandescent lamps and similar'devices which consists in coiling thefilament upon a mandrel wire, uniting the end of the filament to theconductive supports of a mount and afterwards removing the mandrel.

2. The method of manufacturing and mounting coiled filaments forincandescent lamps and similar devices which consists in coiling thefilament upon a mandrel wire, uniting the end of the filament to theconductive supports of a mount, and dissolving out the mandrel.

3. The method of manufacturing and mounting coiled filaments forincandescent lamps and similar devices which consists in coiling thefilament on a mandrel, mounting the filament and then removing themandrel, said filament being given a heat treatment while still on thesaid mandrel.

In witness whereof, I have hereunto set my hand this 6th day ofDecember, 1926.

PERCY A. CAMPBELL.

